In recent years, as semiconductor devices become minute, it becomes necessary to form shallow junctions with high precision, for MOS devices to restrain a short channel effect and for bipolar devices to improve their cutoff frequency fT. One method of forming a shallow junction is a heating method (RTA: Rapid Thermal Annealing) by light irradiation, which is capable of treating a device at a high temperature and for a short time, is employed. Also, the RTA is used for eliminating crystal defects which occur as a result of ion implantation, for various kinds of annealing such as a sinter and the like, and for forming an oxidized film and a nitrificated film. Therefore, it has become very important to accurately control a substrate temperature of a substrate having various film structures, a substrate having various impurity concentrations, and the like.
However, when the substrate heating method employs light irradiation, there are changes in emissivity of a substrate which are dependent on film structure, film quality, impurity concentration, and the like. This results in changes in the quantity of light absorbed (treatment temperature) by the substrate under circumstances where irradiation intensity is constant. Therefore, as a manufacturing process becomes more complex, it is very difficult to control the heated state of a substrate which contains, variations (dispersion of film thickness, film quality, the amount of impurity, structure and the like). Further, the temperature of the substrate changes depending on a change in the light transmission factor of the quartz tube which is employed as the heating apparatus, a change in a reflection factor of the inside wall of the chamber, and a change in the lamp output in terms of time and the like. In order to cope with this problem, closed loop control is under discussion which measures the substrate temperature and feeds back the measured value to control the lamp output is under discussion.
Also, one apparatus for measuring the substrate temperature, there is a radiation thermometer. This radiation thermometer has an advantage in that it can carry out the temperature measurement of the substrate without coming in contact therewith.
Another temperature measuring apparatus is a thermocouple. When the temperature measurement is carried out by a thermocouple, there are methods to get the thermocouple in direct contact with a surface of the substrate and to fix the thermocouple on the surface of the substrate by using a thermally stabilized adhesive, and so on. These methods have advantage in that when the temperature measuring portion (alloy portion) of the thermocouple comes in direct contact with the substrate it is possible to accurately measure the substrate temperature.
As for other temperature measuring apparatuses, an apparatus is disclosed in a Japanese patent application No 4148546 public bulletin, wherein the substrate temperature is indirectly measured by inserting the thermocouple into a covering member made of silicon carbide (SiC).
Temperature measurements made by using the above-mentioned radiation thermometer are different from the contact-type heat measuring method using thermocouples in that its measuring accuracy depends on the surface state of the object to be measured and hence, is strongly influenced by a measuring environment. With substrates having various film structures and impurity concentrations, there is different emissivity for every substrate. Accordingly, as there is a need to first obtain the emissivity of each substrate in order to carry out an accurate measurement.
Also, with the method for measuring substrate temperature by getting the thermocouple in direct contact with the substrate, problems occur with the deterioration in the thermocouple due to a reaction between the substrate and the thermocouple, metal contamination of the substrate, and the like.
Furthermore, with the method for measuring the temperature by inserting the thermocouple into the covering member, a problem of the metal contamination of the substrate by the thermoelectric couple is solved. However, the thermocouple is measuring the temperature of the covering member. Also, in a process wherein the substrate is subjected to heating by light irradiation heating apparatus, when the substrate temperature rises, the covering member is heated not only by thermal conduction, but by directly absorbing the irradiated light. As a result, the accurate measurement of the substrate temperature becomes difficult.
Also, the heat conduction from the substrate, absorption of radiation from the substrate by the covering member, and absorption of the irradiated lamp light differ depending on materials used for the covering member. Quartz and silicon carbide are shown as examples. When the quarts is used for the covering member, the light absorption can be restrained, but because the quartz has body heat conduction, the measurement of the substrate temperature is difficult and its thermal responsiveness deteriorates. On the other hand, when silicon carbide is used for the covering member, it excels in conducting substrate, heat but, because it absorbs a great deal of light, the measured temperature depends greatly on the light irradiation intensity. Due to these thermal characteristics, each of the materials has advantages as well as a drawback.
Another method to increase thermal conduction efficiency from the substrate employs machining the covering member flat at a contact portion between the covering member and the substrate , where two surfaces are in contact with each other, but this method leads to increasing the thermal capacity of the covering member. As a result, there is increased heating due to the direct absorption of light, thereby making it impossible to accurately measure the substrate temperature.
Where closed loop control is used to vary light irradiation intensity, the amount of heat absorbed by the covering changes depending on the irradiation intensity it is, therefore, impossible to accurately measure changes in the light absorption quantity (substrate temperature) due to changes in the irradiation factor of the substrate which has various kinds of film structures and impurity concentration. Furthermore, in the case of a sheath-type thermocouple, because a portion of the thermocouple, other than a point where the temperature is measured is heated, there is a concern that a high temperature region will occur in an middle region with respect to the "temperature measuring point", thereby inviting a shunt error, which drops the accuracy of the measurement.